The object of the present invention is to develop a process for the production of skatylhydantoin by hydrogenation of indolalhydantoin in the presence of a solvent and a hydrogenation catalyst.
Skatylhydantoin is a valuable intermediate product for the production of D,L-tryptophane which can be obtained in good yields by the alkaline hydrolysis of the skatylhydantoin, see White U.S. Pat. No. 2,557,920.
It is already known to hydrogenate indolalhydantoin in caustic soda solution with sodium amalgam, see Majima Berichte Vol. 55 pages 3859-3865, particularly page 3863 (1922). However, only a yield of 68% of theory is produced thereby.
Also it is already known to catalytically hydrogenate indolalhydantoin in caustic soda in the presence of Raney nickel, see Elks, J. Chem. Soc., pages 629 to 632 (London, 1944). In this process, however, the catalyst must be added in an amount of 100 weight percent based on the weight of the material to be hydrogenated and a reaction time of 8 hours is required. If hydrogenation is carried out at 100.degree. to 110.degree. C and a hydrogen pressure of 50 atmospheres in 65 percent aqueous alcohol the reaction time is shortened to 2 hours. However, the yields only amount to 80% of theory, see J. Chem. Soc., loc. cit.
Finally it is also known to treat indolalhydantoin with aqueous ammonium sulfide and simultaneously hydrolyze the skatylhydantoin formed to D,L-tryptophane, see Livak, U.S. Pat. No. 2,435,399. However, the total yield amounts only to 56% of theory.
In all of the known processes, there were used aqueous or water containing solvents through which, particularly at temperatures above 60.degree. C, besides the desired hydrogenation there also occurred saponification reaction which led to reductions in yield because of the formation of the hydroxy or keto analogues of D,L-tryptophane.